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Getting a sense of inches and feet

Explore inches and feet as units of length. Learn to visualize an inch with a quarter or thumb and understand a foot equals 12 inches. The video includes examples of when to use inches or feet for measuring various objects. Created by Sal Khan.

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Video transcript

- [Instructor] In this video, I'm going to introduce you to two units of measuring length. The first is the inch, which you might have heard about. And you're probably thinking, "How long is an inch?" Well, if you're familiar with a quarter, a quarter looks something like this. You see George Washington on it. A quarter is almost an inch. So an inch might be something like that. One inch. Another way to think about it is when I'm looking at my thumb, and I'm a grown man, at least physically (chuckles), my thumb is about two inches in length. So my thumb is about two inches in length. One inch and two inches. Depending on your age, if you're watching this and let's say you're eight years old, seven or eight years old, your thumb might be closer to an inch or maybe a little bit over an inch. Now the other unit of measurement, you can view it as a bunch of inches put together. And if you put 12 inches together, you get what is known as a foot, a foot. Now the word foot is used for many things in our language, including for our individual feet, or the things at the ends of our legs. And I believe, I'm not sure where the unit of measurement of the foot came from, but they might be related because actually my foot is almost a foot. And in fact, my shoes, and I wear a size, I wear a men's size 10 1/2, my sneakers that I wear are almost exactly one foot. And you can sometimes see it written as ft, short for foot. Now, clearly not everyone's foot is exactly a foot 'cause everyone's feet and shoes have different lengths, but that gets you a sense of how large a foot is. Another way to think about it, and as I just mentioned, if you put 12 inches together, you get one foot. 12 inches equals one foot. So let me give you some objects. And I want you to pause the video and think about, would you measure them in foot or inches or whether the measurements themselves sound like measurements in feet or inches. So if I give you a piece of paper, a regular piece of paper, kind with the holes on it and the nice lines. So a piece of paper right over here. If I were to tell you that the height of this paper is 11 something, would that be 11 inches or 11 feet? Well, if was 11 feet, that would be a huge piece of paper. That would be a piece of paper taller than me. That would be more of a carpet than a piece of paper. So a piece of paper, actually a standard piece of paper is 11 inches tall. Now, if we were to go outside and play a little basketball, so this is the basketball, or that's the backboard. And then we have the hoop, the hoop, we have the net, and then we have the post holding it up. Let me draw that in a different color. So we have the post. And this is a standard NBA basketball rim. If I were to say it's 10 something off the ground, is that 10 inches or 10 feet? Well, if it was 10 inches, it would be very easy to dunk a basketball. (chuckles) Although it might be hard to fit the basketball in the rim because if the rim was, it might also be very, very small. That would be more of a basketball goal for an insect of some kind or for a very, very small mouse. For normal human beings, the standard height of a basketball goal is 10 feet. The one that they play with in the NBA. At your school, if you're a little bit younger, you might see a basketball goal that is six feet or eight feet or nine feet. But the standard ones that the professionals play with are 10 feet tall. Now let me give you some things, and I wanna decide whether it's better to measure them with feet or with inches. So let's say that I have a swimming pool, say I have a swimming pool right over here. And that is the pool. Would it be better to measure the length of this swimming pool in feet or in inches? Pause the video and think about that. Well, a swimming pool is fairly large. It is much larger than even a foot. So you'd think you'd want to measure it, if you had to choose between feet and inches, you would pick feet. And so this would be a situation where that pool might be, say, 75 feet long. Now, if you were measuring the length of a mouse, this is a mouse right over here. Not my best drawing of a mouse with its tail, its feet right over there. Would you be best off measuring it in feet or inches? A small mouse, a mouse that could fit in your hand. Well, that's going to be a good bit less than a foot. So it makes sense to measure that in inches. I've seen mice that might only be two or three inches long. So I'll leave you there. Hopefully that gives you a rough sense of what an inch is, what a foot is, how they're related to each other, and when you might use one or the other.